Power supply for controlled parallel charging and discharging of batteries

ABSTRACT

A power supply and switching technique is provided that utilizes a first battery and a second battery to charge a load. The power supply includes a first controlled power switch coupled to the first battery and the load, a second controlled power switch coupled to the second battery and the load, and a power controller coupled to the first controlled power switch, the second controlled power switch and the load. The power controller monitors the voltage and the load and causes a charge to be applied to the load when the load voltage is not a predetermined voltage. The power controller causes a charge to be applied to the load by selectively closing the first controlled power switch, thereby providing a charge from the first battery to the load, and/or selectively closing the second controlled power switch, thereby providing a charge from the second battery to the load. A similar switching technique may be used to recharge the first and second battery by alternately coupling them to an external power source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/799,706, filed Mar. 15, 2004 now U.S. Pat. No. 6,849,966, nowallowed, which is a continuation of U.S. patent application Ser. No.10/058,070, filed Jan. 29, 2002, now U.S. Pat. No. 6,727,602 issued Apr.27, 2004, which claims priority to the following provisionalapplication, which is incorporated by reference in its entirety herein:U.S. Provisional Patent Application Ser. No. 60/264,259, entitled“Battery-Operated Power Supply,” filed Jan. 29, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for operating apower supply. More specifically, the present invention relates to asystem and method for utilizing battery power sources in an electronicpower supply.

2. Background

Conventional electronic power supplies that operate using battery powersources suffer from a number of disadvantages.

For example, a conventional method for providing a DC voltage to a DC-DCconverter utilizes two or more batteries in a series configuration.Often, when batteries are configured serially, one battery will becomedepleted well in advance of the others. This is due, in part, to varyinginternal series resistances as well as other characteristics that maycause each battery to discharge at a different rate. Where one batterydies in advance of the others in a series configuration, no power can bedelivered to the device being powered.

Recharging batteries that are in series can also be problematic. Becausethe batteries in a stack typically discharge at different rates, thevoltage in each battery before recharging will be different. If one ofthe batteries in series has been severely discharged to the point wheregas has started to build on the anode or cathode, that battery canactually reverse polarity. When an attempt is made to recharge thebatteries, the battery with a reverse polarity will, in effect, becharged in reverse. This will result in the death of that battery, whichmeans that no power can be delivered to the device being powered asdiscussed above. Additionally, it has been observed that charging abattery with a reverse polarity can actually cause the battery to bedamaged or heat up to the point where it will explode.

Furthermore, when batteries are arranged in series, it is difficult tomonitor how much charge is in each of them. Because batteries aremanufactured with slight differences, each individual battery willcharge and discharge it a different rate. It would be useful to know fordischarging and recharging purposes how much charge remains in eachbattery in a battery pack. In a conventional series arrangement, theoverall voltage coming out of a battery pack may be detected, but it isimpossible to determine the state of one of the cells in the middle ofthe stack.

Conventional schemes for operating two or more battery cells in parallelare also disadvantageous in that they require the addition of externalparts to add multiple cells to a battery pack, which can be complex andcostly. Moreover, conventional techniques for operating cells inparallel do not avoid the problem of over-discharging, or “deep”discharging of a battery that can result in polarity reversal.

A further disadvantage of conventional battery-operated power suppliesis that they utilize separate power control chips that must be coupledto the application to be powered using external logic and parts. Thismakes the design more expensive. Furthermore, because these separatepower control chips are not “on chip” with the application beingpowered, they do not have access to a priori information about impendingload changes. Thus, conventional battery-operated power supplies requirelarge load capacitors to act as charge buffers to prevent sudden loadchanges from pulling a supply voltage out of specification (in the casewhere a large load is suddenly presented) or from causing the supplyvoltage to spike too high (in the case where the load current issuddenly turned off).

Conventional battery-operated power supplies also do not monitor thestate of batteries by determining how much charge is in them, butinstead simply look at the voltage on the battery. Although the voltageon the battery provides an indication of the state of the battery, thatinformation is not as useful as tracking how much charge remains in thebattery.

Conventional battery-operated power supplies are also disadvantageous inthat they typically utilize a Schottky diode to discharge current into aload. Because a Schottky diode has a typical turn-on voltage of about0.4 to 0.6 volts, the use of the diode will result in an energy lossequal to the turn-on voltage times the load current. This is lost energythat could have otherwise been used by the load. Where only one or twosmall batteries are being used, this loss can be quite significant. Theuse of Schottky diodes is also problematic because it is impossible tocontrol their turn-on and turn-off characteristics beyond theirmanufactured values.

BRIEF SUMMARY OF THE INVENTION

There is a great need for innovative techniques that would enableportable electronic equipment to operate more efficiently from batterypower sources. For example, in the Bluetooth™ area of wireless products,it is anticipated that there will be great demand forBluetooth™-compatible headsets. High efficiency and small size areessential to the success of any Bluetooth™ headset. A battery-operatedpower supply is used to power the headset at the correct voltage fromrechargeable batteries.

The present invention provides a system and method for drawing chargefrom two or more batteries under the control of a power controller,wherein the power controller may control and monitor the amount and rateof discharge. The present invention may also be used to recharge two ormore batteries under the control of a power controller, wherein thepower controller may control and monitor the amount and rate ofcharging. In an embodiment, the present invention may be used to providepower to a DC to DC converter and to recharge batteries used forproviding power to a DC to DC converter.

The present invention is advantageous in that it provides a separateconnection to each battery for charging and recharging purposes. As aresult, the depletion of any single cell in a battery pack will notresult in a complete loss of power to the application being powered, ascharge may be drawn from any of the other cells that have not yet beendepleted. In fact, the power controller of the present invention may beused to increase the power drawn from the surviving cells to compensatefor the loss of the depleted batter.

Because embodiments of the present invention provide a separateconnection to each battery, the state of each battery may be monitoredon an individual basis. As a result, each cell can be charged anddischarged in an optimal way. For example, polarity reversal may beavoided by tracking the amount of charge that has been drawn off of eachbattery in the battery pack. Additionally, discharging and rechargingmay be evenly applied to each cell. Optimal charging and discharging ofeach battery will permit the battery to last through morecharge/discharge cycles, hold more power before needing charging, and befar more reliable than batteries in conventional power supplies.

Also, because each battery may be monitored on an individual basis,embodiments of the present invention also permit information to beprovided to the user about the state of each battery, such as a warningwhen a battery's charge is low or when a battery is depleted.

In an embodiment of the present invention, the state of each battery ismonitored by utilizing counters that maintain a continuous running totalof how long the battery has been charged or discharged. Thisinformation, in turn, may be used to determine the precise amount ofcharge remaining in each battery. This technique represents animprovement over conventional power supply circuits, in which the statusof a battery or batteries is determined simply by looking at the voltageof a battery or batteries.

The present invention is also advantageous in that it permits theaddition of multiple cells in a battery pack with a very minimalexternal parts count, while still keeping the cells separate so thatcharging can be optimized and so that the depletion of individual cellsdying in the battery pack will not cause a loss of power to the entireproduct. As a result, embodiments of the present invention may beimplemented in an easy and inexpensive manner.

Another benefit of the present invention is that it may be implementedvery efficiently on-chip along with an application circuit beingpowered. For example, an embodiment of the present invention isimplemented on-chip With an application circuit in CMOS. Since anembodiment of the present invention ma) be implemented in digital CMOSdigital logic may be easily added to the power controller that willallow fine tuning of the rate of charge/discharge of a given battery inlight of battery condition and load demands.

Also, since embodiments of the present invention may be implementedon-chip with the application circuit being powered, the applicationcircuit can provide useful information to the power controller to helpcontrol the power supply. For example, the application circuit canprovide the power controller with a priori information about animpending load change. This may occur, for instance, where theapplication circuit is going from a standby state to an active state, orvice-versa. The access to information regarding impending load changespermits the power controller to control the power supply to increase ordecrease the power supply accordingly in advance of the change. As aresult, embodiments of the present invention do not require the largeload capacitors of conventional designs that act as charge buffers whichcompensate for large and sudden load changes.

Additionally, embodiments of the present invention use a controlled FETto discharge current into a load, and thus avoid the energy lossassociated with conventional designs that use a Schottky diode toperform that function. This is due to the fact that a FET may have adrain-to-source voltage that is significantly lower than the turn-onvoltage of a Schottky diode. For example, a FET with a drain-to-sourcevoltage of 10 mV may be used as compared to a Schottky diode with atypical turn-on voltage of 0.4 to 0.6 V. Furthermore, the use of a FETin embodiments of the present invention permits precise control ofturn-off and turn-on voltages as opposed to Schottky diodes, in whichthe turn-on and turn-off voltages cannot be modified after manufacture.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the system and method particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a artof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable person skilled in the pertinent art to make anduse the invention.

FIG. 1 is a functional block diagram of a battery-operated power supplyin accordance with an embodiment of the present invention.

FIG. 2 is a high-level schematic of a battery-operated power supplycircuit in accordance with embodiments of the present invention.

FIG. 3 is a functional block diagram of a power control circuit used ina battery-operated power supply in accordance with an embodiment of thepresent invention.

FIG. 4 depicts exemplary voltages and charge values for components of abattery-operated power supply circuit in accordance with an embodimentof the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements. Additionally, the left-mostdigit(s) of a reference number identifies the drawing in which thereference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 depicts a functional block diagram of a battery-operated powersupply 100 in accordance with an embodiment of the present invention.Power supply 100 includes a first battery 101 (designated “B₁,”), afirst inductor 102 (designated “L₁”), a second battery 104 (designated“B₂”), a second inductor 105 (designated “L₂”), a load 107, a powercontroller 108, a first controlled power switch 103, a second controlledpower switch 106, and an optional external power supply 109. Inembodiments, the power supply 100 generates the necessary power tooperate a connected application device or circuit, which is representedschematically as load 107. In other words, the power supply 100 isdesigned to make sure that the battery voltage provided by the first andsecond batteries 101 and 104 is matched to the voltage of the circuit inwhich those batteries are employed.

Each battery 101 and 104 is separately coupled to the load 107 via thefirst and second controlled power switches 103 and 106, respectively.When the first controlled power switch 103 is open, charge from thefirst battery 101 accumulates on the first inductor 102, and when thefirst controlled power switch 103 is closed, charge is delivered fromthe first battery 101 to the load 107. In a like fashion, when thesecond controlled power switch 106 is open, charge from the secondbattery 104 accumulates on the second inductor 104, and when the secondcontrolled power switch 106 is closed, charge is delivered from thesecond battery 104 to the load 107.

The opening and closing of the controlled power switches is selectivelycontrolled by the power controller 108. The power controller 108 isresponsible for maintaining the necessary operating voltage across load107. To do so, the power controller 108 determines what the actualvoltage is across the load 107, to which it is connected. If the voltageacross the load 107 is less than the voltage necessary for powering theapplication device or circuit, the power controller 108 operates toincrease the charge delivered from the first battery 101 and/or thesecond battery 104. If the voltage across the load 107 is more thanrequired for powering the application device or circuit, the powercontroller 108 operates to decrease the charge delivered from the firstbattery 101 and/or the second battery 104.

The power controller 108 increases the charge delivered from the firstbattery 101 by increasing the amount of time that the first controlledpower switch 103 is closed and decreases the charge delivered from thefirst battery 101 by increasing the amount of time that the firstcontrolled power switch 103 is open. Similarly, the power controller 108increases the charge delivered from the second battery 104 by increasingthe amount of time that the second controlled power switch 106 is closedand decreases the charge delivered from the second battery 104 byincreasing the amount of time that the second controlled power switch106 is open.

In embodiments, the controlled power switches 103 and 106 may be openand closed in an alternating fashion by the power controller 108, sothat charge is delivered from only one battery at a time. Alternately,the controlled power switches 103 and 106 may be closed at the sametime, so that power is delivered from both batteries at once. In furtherembodiments, the power controller 108 may control the controlled powerswitches 103 and 106 to discharge in an alternating fashion as well assimultaneously.

The design depicted in FIG. 1 is advantageous in that it provides aseparate connection between each battery 101 and 104 to the load 107 fordischarging purposes. As a result, the depletion of either battery 101and 104, in and of itself, will not result in a complete loss of powerto the application device or circuit being powered, as represented bythe load 107. In embodiments, the power controller 108 increases thedischarge rate from the surviving battery to compensate for the loss ofthe depleted battery.

Furthermore, because the design depicted in FIG. 1 provides a separateconnection between each battery 101 and 104 and the load 107, the stateof each battery 101 and 104 can be monitored on an individual basis. Forexample, polarity reversal may be avoided by tracking the amount ofcharge that has been drawn off of the first battery 101 and the secondbattery 102. Additionally, the power controller 108 can operate toensure that discharging occurs evenly as between battery 101 and 104.

The design show n in FIG. 1 can also be utilized to implement arecharging technique for the power supply 100. As shown in FIG. 1, thepower supply 108 also includes an optional external power supply 109which may be used to recharge the first battery 101 and the secondbattery 104. In an embodiment, charge from the external power supply 109may be selectively applied to each battery 101 and 104 via operation ofthe controlled power switches 103 and 106, respectively. In such anembodiment, when the first controlled power switch 103 is open, nocharge from the external power supply 109 will be supplied to the firstbattery 101, and when the first controlled power switch 103 is closed,charge from the external power supply 109 is delivered to the firstbattery 101. In a like fashion, when the second controlled power switch106 is open, no charge from the external power supply will be suppliedto the second battery 104, and when the second controlled power switch106 is closed, charge from the external power supply 109 will bedelivered to the second battery 104.

As discussed above, the opening and closing of the controlled powerswitches is selectively controlled by the power controller 108. In arecharging scheme, the power controller 108 is responsible for providingenough charge to the first and second batteries 101 and 104 so that theywill remain sufficiently charged to power a connected application deviceor circuit. To do so, the power controller 108 determines how muchcharge remains in each battery. If one of the batteries requiresrecharging, the power controller 108 operates to increase the chargedelivered to that battery. Alternately, if a battery is sufficientlyrecharged, the power controller 108 operates to decrease or stop thecharge being delivered to that battery.

In a recharging scheme, the power controller 108 increases the chargedelivered to the first battery 101 from the external power supply 109 byincreasing the amount of time that the first controlled power switch 103is closed and decreases the charge delivered to the first battery 101from the external power supply 109 by increasing the amount of time thatthe first controlled power switch 103 is open. Similarly, in arecharging scheme, the power controller 108 increases the chargedelivered to the second batter) 104 from the external power supply 109by increasing the amount of time that the second controlled power switch106 is closed and decreases the charge delivered to the second battery104 from the external power supply 109 by increasing the amount of timethat the second controlled power switch 106 is open.

As discussed above, the state of each battery 101 and 104 may bemonitored on an individual basis by the power controller 108. As aresult, the power controller 108 can control the rate and amount ofrecharging of each battery by the external supply 109 such that eachbattery is recharged in an optimal way. For example, the powercontroller 108 can operate to ensure that recharging is even applied tobatteries 101 and 104.

The power supply 100 of FIG. 1 utilizes only two batteries 101 and 104.However, as will be appreciated by persons of ordinary skill in therelevant art(s) from the teachings provided herein, the discharging andrecharging techniques discussed herein may be applied in a power supplywith only one battery, with two batteries, or with more than twobatteries. For example, the power supply 100 of FIG. 1 could be modifiedto include an additional battery in parallel with the first battery 101and the second battery 104 by adding an additional inductor andcontrolled power switch. The present invention includes such alternateembodiments.

FIG. 2 illustrates a high-level schematic of a battery-operated powersupply circuit 200 in accordance with embodiments of the presentinvention. The power supply circuit 200 includes a battery 201, a shuntcapacitor 202, an inductor 207, a controlled power switch 211, a loadcapacitor 205 and a load 206. The load 206 represents an applicationdevice or circuit to which the power supply circuit 200 is connected andfor which the power supply circuit 200 provides operating power. In theembodiment shown in FIG. 2, the battery 201 is a 1.2 volt battery andthe load 206 is 1.8 volts. In embodiments, the battery 201 may comprisea nickel cadmium (NiCd) battery or a nickel-metal hydride battery.

In the power supply circuit 200, the battery 201 and the inductor 207are analogous to either the first battery 101 and the first inductor 102or the second battery 104 and the second inductor 105 of the powersupply 100 of FIG. 1. The load 206 is analogous to the load 107 of thepower supply 100 of FIG. 1. Finally, the controlled power switch 211 isanalogous to either of the controlled power switches 103 and 106 of thepower supply 100 of FIG. 1.

In the embodiment shown in FIG. 2, the controlled power switch 211includes a first transistor 203, a second transistor 204, a thirdtransistor 209, a fourth transistor 212, a V_(BOOST) node 208, and aV_(DD) node 210. In embodiments, the transistors 203, 204, 209 and 212are implemented as FETs.

The power supply 200 provides charge from the battery 201 to the load206 via the operation of the controlled power switch 211. The operationof the controlled power switch 211 is, in turn, controlled by theapplication of control signal V_(N) to the first transistor 203 andapplication of control signal V_(P) to the second transistor 204 and thefourth transistor 212. The technique by which the control signals V_(N)and V_(P) are generated will be discussed in more detail below in regardto FIG. 3.

In the controlled power switch 211, when the control signal V_(N)applied to the first transistor 203 goes high, a charge I_(L) ispermitted to build up on the inductor 207. This is depicted, forexample, in FIG. 4, which shows the control signal V_(N) as signal 401and the charge I_(L) on the inductor 207 as signal 403. As can be seenin FIG. 4, when V_(N) goes high, a charge I_(L) builds up on theinductor 207.

When the control signal V_(P) applied to the second transistor 204 andthe fourth transistor 212 subsequently goes high, the charge I_(L) onthe inductor 207 is provided to the load 206. This is depicted, forexample, in FIG. 4, which shows the control signal V_(P) as signal 402and the charge I_(L) on the inductor 207 as signal 403. As can be seenin FIG. 4, when V_(P) goes high, the charge I_(L) on the inductor 207 isdischarged to the load 206.

The use of third transistor 209 as opposed to a Schottky diode forcontrolling discharge into the load represents an improvement overconventional power supplies. This is due to the fact that the thirdtransistor 209 may have a drain-to-source voltage that is significantlylower than the turn-on voltage of a Schottky diode. For example, thethird transistor 209 may be implemented as a FET with a drain-to-sourcevoltage of 10 mV as compared to a Schottky diode that has a typicalturn-on voltage of 0.4 to 0.6 V. Because a Schottky diode has a typicalturn-on voltage of about 0.4 to 0.6 volts, the use of the diode willresult in an energy loss equal to the turn-on voltage times the loadcurrent. This is lost energy that could have otherwise been used by theload. Furthermore, the use of the third transistor 209 in embodiments ofthe present invention permits precise control of turn-off and turn-onvoltages as opposed to Schottky diodes, in which the turn-on andturn-off voltages cannot be modified after manufacture.

The voltage V_(BOOST) that accumulates on node 208 indicates the currentvoltage level of the battery. In embodiments, the voltage at V_(BOOST)may be used to monitor the state of the battery 201 and to ensure thatthe battery 201 has not been completely discharged or entered into astate of reverse polarity. For example, the power controller 108 of thepower supply 100 of FIG. 1 could monitor the voltage V_(BOOST).

The voltage V_(DD) that appears at node 210 of power supply circuit 200indicates the voltage across the load 206 (the “load voltage”).

In the power supply circuit 200, the shunt capacitor 202 is provided inparallel with the battery 201 to act as a shunt in case there is anyinductive “back-kick” onto the battery, as will be understood by thoseskilled in the art. Additionally, the load capacitor 205 is provided inparallel with the load 206 to act as a charge buffer in the instance ofsudden load changes. As is further discussed herein, embodiments of thepresent invention permit the use of a very small load capacitor (e.g.,10 μF) as compared to the load capacitors used in conventional powersupply circuits.

The power supply circuit 200 of FIG. 2 is shown using only one battery,201. However, as will be appreciated by persons of ordinary skill in therelevant art(s) from the teachings provided herein, the power supplycircuit 200 of FIG. 2 could be modified to use two or more batteries.For example, this could be achieved by connecting an identicalconfiguration of shunt capacitor 202, inductor 207, controlledpower-switch 211, and load capacitor 205 in parallel to the load 206 foreach battery to be added.

FIG. 3 is a functional block diagram of a power control circuit 300 thatcomprises a part of a power controller used in a power supply inaccordance with an embodiment of the present invention. The powercontrol circuit 300 monitors the load voltage and controls the operationof a controlled power switch in power supply circuit embodiments of thepresent invention. For example, the power control circuit 300 may beused to control the operation of the controlled power switch 211 in thepower supply circuit 200 of FIG. 2. Also, in an embodiment, the powercontrol circuit 300 of FIG. 3 may comprise part of the power controller108 of FIG. 1.

The power control circuit 300 includes a clock 301, a comparator 302, adigital control module 303, a V_(P) counter 306, and a V_(N) counter307. In an embodiment, the components of the power control circuit 300are entirely implemented as digital components. For example, thecomponents of the power control circuit 300 may be implemented indigital CMOS.

The comparator 302 is used by the power control circuit 300 to determineif the voltage across the load, V_(DD), is sufficient to power theattached application circuit or device. In the power control circuit300, the comparator makes this determination by comparing V_(DD)/2 to areference voltage, V_(REF), that is equal to the desired operatingvoltage divided by 2. The input V_(DD)/2 may be generated by running theoutput voltage-V_(DD) through a simple resistor divider network or acapacitor divider network. The reference voltage V_(REF) may be obtainedby a bandgap reference circuit or other circuit known to persons skilledin the art for generating reference voltages. As an example, in thepower supply circuit 200 of FIG. 2, the desired operating voltage is 1.8volts. Therefore, an appropriate value or V_(REF) would be 0.9 volts.

By comparing the load voltage V_(DD) to the reference voltage V_(REF),the comparator 302 provides an indication to the digital control module303 of whether the load voltage-V_(DD) is above or below the desiredlevel. In response, the digital control module 303 uses this informationto generate control signals V₁ and V_(N) in a manner that will eitherincrease or decrease the amount of charge delivered to the load in orderto achieve the desired voltage level.

As will be appreciated by persons skilled in the art, a wide variety ofcomparators 302 may be used to monitor the level of the load voltageV_(DD). Additionally, more than one comparator may be used. For example,in an embodiment, one window comparator could be used to determine ifV_(DD) is very close to the desired level, so that only minormodifications to the control signals V_(P) and V_(N) need be made, whilean additional two comparators could be used to determine if V_(DD) ismuch further away from the desired level, such that greatermodifications to the control signals V_(P) and V_(N) need be made.

In a further embodiment, the clock 301 is used to provide timingformation to the digital control module 303, and a determination is madeas to how long the load voltage V_(DD) has been above or below thedesired supply level. The digital control module 303 then modifies thecontrols signals V_(P) and V_(N) accordingly, so that the load voltageV_(DD) will be increased or decreased in greater proportion depending onhow long V_(DD) has been away from the desired supply.

The digital control module 303 generates the control signals V_(P) andV_(N) that control the operation of a controlled power switch in a powersupply in accordance with embodiments of the present invention. Forexample, the digital control module 303 may generate the control signalsV_(P) and V_(N) that control the operation of the controlled powerswitch 211 in the power supply 200 of FIG. 2.

In an embodiment, the control signals V_(P) and V_(N) each comprise aseries of pulses of a fixed pulse width and the digital control module303 controls the frequency of the pulses for each signal. In otherwords, the digital control module 303 controls the number of intervalsbetween pulses in the signals V_(P) and V_(N). By increasing thefrequency of the pulses, the digital control module 303 can increase theamount of time that the controlled power switch discharges the batteryinto the load. Alternately, by decreasing the frequency of the pulses,the digital control module 303 can decrease the amount of time that thecontrolled power switch discharges the battery into the load. Forexample, in order to pull charge out of the battery only 50% of thetime, the digital control module 303 will generate V_(P) and V_(N)signals in which every pulse is followed by a time off equal to thepulse width. As a further example, if only 25% discharging is required,the digital control module 303 will generate V_(P) and V_(N) signals inwhich every pulse is followed by a time off equal to three pulse widths.

In order to generate the control signals V_(P) and V_(N) at a fixedfrequency the digital control module 303 uses the clock 301 as areference. In embodiments, the clock 301 operates at 12 MHz. In afurther embodiment, the digital control module 303 generates the controlsignals V_(P) and V_(N) at the same frequency in order to avoid creatingharmonics in the power supply circuit that may interfere with aconnected application device or circuit.

Persons skilled in the relevant art will appreciate that the digitalcontrol module 303 may implement other algorithms for generating thecontrol signals V_(P) and V_(N) in order to increase or decrease theamount of time that the controlled power switch discharges the batteryinto the load. For example, in an alternate embodiment, the digitalcontrol module 303 can alter the pulse width of the control signalsV_(P) and V_(N) in order to increase or decrease the amount of time thatthe controlled power switch discharges the battery into the load. Thepresent invention is directed to such other algorithms.

In an embodiment, the power control circuit 300 is implemented on thesame chip as the application circuit energized by the power supply. Forexample, the power control circuit 300 may be implemented along with theapplication circuit in digital CMOS. In an implementation of this type,the application circuit may provide the digital control module 303 witha priori information about an impending load change. For example, theapplication circuit may provide the digital control module 303 withinformation about an impending increase or decrease in the load. Whenthe digital control module 303 receives this advanced information aboutthe application circuit, it can adjust the control signals V_(P) andV_(N) accordingly to increase or decrease the output voltage V_(DD).Because the digital control module can receive advance information aboutload changes from the application circuit, a power supply using thepower controller does not require a large capacitor in parallel with theload to act as a charge buffer for dealing with sudden load changes.

In the power control circuit 300, the V_(P) counter 306 accumulatesinformation about the control signal V_(P), including how long V_(P) hasbeen turned on. Similarly, the V_(N) counter 307 accumulates informationabout the control signal V_(N), including how long V_(N) has been turnedon. The counters 306 and 307 scale this information with appropriatescaling factors (such as factors relating to the size of the inductorand load capacitor attached to the controlled power switch controlled bythe control signals V_(N) and V_(P)) to determine precisely how muchcharge has been removed from the battery whose discharge is controlledby the control signals V_(N) and V_(P).

The counters 308 and 309 can thus report the status of the battery tothe user via an LED or other display. For example, the counters 308 and309 may provide a warning to the user when a battery's charge is low orwhen a battery is depleted. In an alternate embodiment, the counters 308and 309 provide information about the status of the battery to thedigital controller 303, which can se the information to determinewhether to modify the control signals V_(N) and V_(P). For example, inan instance where the counters 308 and 309 determine that the battery isclose to depletion or has been completely discharged, the digitalcontrol module 303 can turn off V_(N) and V_(P) to ensure that no morecharge is removed from the battery.

In embodiments, the counter 306 and 307 are implemented as simpledigital counters controlled by the clock 301.

It will be appreciated by, persons of ordinary skill in the art from theteachings provided herein that the power control circuit 300 of FIG. 3may also be used to implement a battery recharging scheme. In rechargingembodiments of the present invention; the power control circuit 300 isused to monitor the state of a battery (as opposed to monitoring a loadvoltage) and to generate control signals V_(N) and V_(P) to control theamount and rate of charge provided to the battery (as opposed to theload). The invention is directed to such recharging schemes.

In an embodiment, a system using a battery-operated power supply of thetype described herein can provide new and useful configurations forproducts. For example, a system such as a headset can be built inmodules. The headset could comprise two pieces: a basic monaural version(single headphone) with the electronics and a battery built in, and asecond headphone for stereo use. If a user wants to use the headset as astereo headset, he can attach the second headphone, which has its ownbattery. Stereo mode would require more power and the second headphonewould provide that power. Configuring the power supply to operate off ofany number of cells or batteries in parallel, as described herein,provides a new level of flexibility in product design and configuration,which is difficult to do with batteries running in series. A system canbe made in modules, each with its own battery, which can be placed inparallel with the batteries in other modules. A power controller, suchas the power controller 108 described in reference to FIG. 1, can thenprovide balancing of the available power from the plurality of batteriesto match the plurality of loads.

While specific embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. It will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedin the appended claims. Thus, the breadth and scope of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A power control circuit that controls the amount of charge deliveredfrom a battery to a load, comprising: a comparator that compares avoltage across the load with a desired operating voltage; a controlmodule that generates one or more control signals for controlling therate at which a power switch transfers charge between the battery andthe load responsive to an output from the comparator; wherein thecontrol module generates one or more control signals that increase therate at which the power switch transfers charge between the battery andthe load responsive to an output from the comparator indicating that thevoltage across the load exceeds the desired operating voltage, andwherein the control module generates one or more control signals thatdecrease the rate at which the power switch transfers charge between thebattery and the load responsive to receiving an output from thecomparator indicating that the voltage across the load is less than thedesired operating voltage.
 2. The power control circuit of claim 1,wherein the comparator compares a voltage across the load with a desiredoperating voltage by comparing V_(DD)/2 to V_(DD)/2 is approximatelyequal to the voltage across the load divided by 2, and wherein V_(REF)is approximately equal to the desired operating voltage divided by
 2. 3.The power control circuit of claim 1, wherein the comparator and thecontrol module are implemented as complementarymetal-oxide-semiconductor (CMOS) digital logic.
 4. The power controlcircuit of claim 1, wherein the control module generates a first controlsignal that controls the amount of time that a charge from the batteryis permitted to accumulate within the power switch and a second controlsignal that controls the amount of time that the accumulated charge ispermitted to discharge from the power switch to the load.
 5. The powercontrol circuit of claim 4, wherein the first and second control signalseach comprise a series of pulses having a fixed pulse width, wherein thecontrol module increases the pulse frequency of at least one of thefirst and second control signals to increase the rate at which the powerswitch transfers charge between the battery and the load, and whereinthe control module decreases the pulse frequency of at least one of thefirst and second control signals to decrease the rate at which the powerswitch transfers charge between the battery and the load.
 6. The powercontrol circuit of claim 4, wherein the first and second control signalseach comprise a series of pulses having a fixed frequency, wherein thecontrol module increases the pulse width of at least one of the firstand second control signal to increase the rate at which the power switchtransfers charge between the battery and the load, and wherein thecontrol module decreases the pulse width of at least one of the firstand second control signals to decrease the rate at which the powerswitch transfers charge between the battery and the load.
 7. The powercontrol circuit of claim 1, further comprising: a reference clockcoupled to the control module; wherein the control module receivestiming information from the reference clock and, based on the timinginformation and an output from the comparator, determines an amount oftime that the voltage across the load exceeds or is less than thedesired operating voltage.
 8. The power circuit of claim 7, wherein thecontrol module generates the one or more control signals based on theamount of time that the voltage across the load exceeds or is less thanthe desired operating voltage.
 9. The power control circuit of claim 1,wherein the control module is coupled to an application circuit toreceive information about an impending load change; wherein the controlmodule generates one or more control signals that increase the rate atwhich the power switch transfers charge between the battery and the loadresponsive to receiving information from the application circuit aboutan impending increase in the load, and wherein the control modulegenerates one or more control signals that decrease the rate at whichthe power switch transfers charge between the battery and the loadresponsive to receiving information from the application circuit aboutan impending decrease in the load.
 10. The power control circuit ofclaim 1, further comprising: one or more counters that accumulate theinformation concerning the one or more control signals generated by thecontrol module.
 11. A method for controlling the amount of chargedelivered from a battery to a load, comprising: comparing a voltageacross the load with a desired operating voltage and generating acomparison output; and generating one or more control signals forcontrolling the rate at which a power switch transfers charge betweenthe battery and the load responsive to the comparison output; whereingenerating one or more control signals comprises generating one or morecontrol signals that increase the rate at which the power switchtransfers charge between the battery and the load responsive to acomparison output indicating that the voltage across the load exceedsthe desired operating voltage; and generating one or more controlsignals that decrease the rate at which the power switch transferscharge between the battery and the load responsive to a comparisonoutput indicating that the voltage across the load is less than thedesired operating voltage.
 12. The method of claim 11, wherein comparinga voltage across the load with a desired operating voltage comprisescomparing V_(DD)/2 to V_(DD)/2 is approximately equal to the voltageacross the load divided by 2, and wherein V_(REF) is approximately equalto the desired operating voltage divided by
 2. 13. The method of claim11, wherein generating one or more control signals comprises: generatinga first control signal that controls the amount of time that a chargefrom the battery is permitted to accumulate within the power switch; andgenerating a second control signal that controls the amount of time thatthe accumulated charge is permitted to discharge from the power switchto the load.
 14. The method of claim 13, wherein the first and secondcontrol signals each comprise a series of pulses having a fixed pulsewidth, wherein generating one or more control signals that increase therate at which the power switch transfers charge between the battery andthe load comprises increasing the pulse frequency of at least one of thefirst and second control signals, and wherein generating one or morecontrol signals that decrease the rate at which the power switchtransfers charge between the battery and the load comprises decreasingthe pulse frequency of at least one of the first and second controlsignals.
 15. The method of claim 13, wherein the first and secondcontrol signals each comprise a series of pulses having a fixedfrequency, wherein generating one or more control signals that increasethe rate at which the power switch transfers charge between the batteryand the load comprises increasing the pulse width of at least one of thefirst and second control signals, and wherein generating one or morecontrol signals that decrease the rate at which the power switchtransfers charge between the battery and the load comprises decreasingthe pulse width of at least one of the first and second control signals.16. The method of claim 11, further comprising: receiving timinginformation; and determining an amount of time that the voltage acrossthe load exceeds or is less than the desired operating voltage based onthe timing information and the comparison output.
 17. The method ofclaim 16, wherein generating one or more control signals responsive tothe comparison output comprises generating one or more control signalsresponsive to the amount of time that the voltage across the loadexceeds or is less that the desired operating voltage.
 18. The method ofclaim 11, further comprising: receiving information about an impendingload change; and generating the one or more control signals forcontrolling the rate at which the power switch transfers charge betweenthe battery and the load responsive to the information about theimpending load change.
 19. The method of claim 11, further comprising:accumulating information concerning the one or more control signals. 20.A device, comprising: an application circuit; a power supply; and aswitch coupled between the power supply and the application circuit;and; a power control circuit coupled to the application circuit and theswitch, the power control circuit comprising: a comparator that comparesa voltage utilized by the application circuit with a desired operatingvoltage; a control module that generates one or more control signals forcontrolling the rate at which the switch transfers charge between thepower supply and the application circuit responsive to an output fromthe comparator; wherein the control module generates one or more controlsignals that increase the rate at which the switch transfers chargebetween the power supply and the application circuit responsive toreceiving an output from the comparator indicating that the voltageutilized by the application circuit exceeds the desired operatingvoltage and, wherein the control module generates one or more controlsignals that decrease the rate at which the switch transfers chargebetween the power supply and the application circuit responsive toreceiving an output from the comparator indicating that the voltageutilized by the application circuit is less than the desired operatingvoltage.